A biocide is any substance that kills microorganisms such as bacteria, molds, algae, fungi or viruses. A biostatic is any substance that inhibits the growth of these organisms. The collective group is called antimicrobials. People have been utilizing antimicrobials, commonly called preservatives, since they first discovered a need to extend the useful life of their food as well as their possessions. Sea salt may have been the first antimicrobial used to preserve food. The mummification techniques employed by early Egyptians used to preserve the human and animal body used salts, a variety of resins and the herb Thyme. These preservatives were thought to possess magical powers, as well as the ability to install qualities of eternal life.
The existence of microorganisms in nature was discovered in the late 1600s with the invention of the microscope. As early as 1705, mercuric chloride was used to preserve ships' planking against shipworm. It was not until the 19th century discoveries by Pasteur, Gram and others that the causative agents of microbiological deterioration were understood, although use of antimicrobials in a cause and effect relationship with microorganisms is less than a century old.
A wide range of natural organic compounds are used as antimicrobials. Organic acids are used widely as antimicrobials in food products, e.g. lactic acid, citric acid, acetic acid, and their salts, either as ingredients, or as disinfectants. For example, beef carcasses often are sprayed with acids, and then rinsed or steamed, to reduce the prevalence of E. coli. 
Traditional healers long have used plants to prevent or cure infectious disease. Many of these plants have been investigated scientifically for antimicrobial activity, and a large number of plant products have been shown to inhibit the growth of pathogenic microorganisms. A number of these agents appear to have structures and modes of action that are distinct from those of the antibiotics in current use, suggesting that cross-resistance with agents already in use may be minimal. So, it is worthwhile to study plants and plant products, such as essential oils and extracts for activity against resistant bacteria, viruses, fungi and mold.
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds obtained from the leaves, bark, stems, flowers and berries of plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the “oil of” the plant from which they were extracted, such as oil of thyme. An oil is “essential” in the sense that it carries a distinctive scent, or essence, of the plant, and not that it is essential to life.
Essential oils are generally extracted by distillation, often by using steam. Other processes include expression or solvent extraction, including supercritical CO2. They are used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, for aromatherapy and as natural, renewable antimicrobials.
Many essential oils included in pharmacopoeias possess antimicrobial activity, including but not limited to: oils of bay, cedar, cinnamon, citronella, clove, eucalyptus, garlic, geranium, lavender, leleshwa, lemon, lemongrass, mint neem, black cumin, onion, oregano, peppermint, rosemary, sandalwood, sesame, tea tree and thyme.
Essential oils that are listed as edible include: almond oil (bitter), anise oil, bergamot oil, camphor oil, caraway oil, cassia oil, cedar leaf oil, cedarwood oil, cinnamon oil, citronella oil, clove oil, cornmint oil (Mentha arvensis), eucalyptus oil, geranium oil, grapefruit oil, lavender oil (spike), lemon oil, lemongrass oil, lignaloe (bois derose oil), lime oil, neroli (orange lower oil), nutmeg oil, onion and garlic oil, mint oil, orange oil, oregano oil, origanum oil, orris oil, palmarosa oil, patchouli oil, peppermint oil (Menthapzperita) pettigrainolpine oil, pine needle oil, rose oil (attar of roses), rosemary oil, sandalwood oil, sassafras oil, sesame oil, spearmint oil, thyme oil, vetiver oil, and ylang ylang oil.
Therefore, some of the essential oils that are both edible and have antimicrobial properties include cedar, cinnamon, citronella, clove, eucalyptus, garlic, geranium, lavender, lemon, lemongrass, mint, oregano, peppermint, rosemary, sesame and thyme oils.
Essential oils that are recognized by the US Environmental Protection Agency as minimum risk active pesticides under section 25(b) of the Federal Insecticide, Fungicide & Rodenticide Act (FIFRA) are cedar, cinnamon, citronella, clove, garlic, geranium, lemongrass, mint, peppermint, sesame, and thyme oils.
The antimicrobial properties of 21 essential oils and two plant essences were investigated against five food-borne pathogens. The maximum bacteriostatic concentration was 0.075%, with the oils of bay, cinnamon, clove and thyme being the most potent (ref: A. Smith-Palmer, J. Stewart and L. Fyfe. Antimicrobial properties of plant essential oils and essences against five important food-borne pathogens. Letters in Applied Microbiology 1998. 26. 118-122).
Oil of thyme, the essential oil of the common herb thyme (Thymus vulgaris), contains 20-54% thymol. Thyme essential oil also contains a range of additional compounds, such as p-cymene, myrcene, borneol and linalool. Before the advent of modern antibiotics, oil of thyme was used to medicate bandages. Thymol, a powerful antiseptic, is the main active ingredient in various commercially produced mouthwashes. Thymol has also been shown to be effective against various fungi that commonly infect toenails. Thymol can also be found as the active ingredient in some all-natural, alcohol-free hand sanitizers and hard surface disinfectants such as Scotch-Brite Disinfectant Wipes where the active ingredient is 0.05% thymol as a component of thyme oil.
Microemulsion technology has been in existence for many years. In fact, many commercial microemulsion products are found in the marketplace including floor polishes and cleaners, personal care products, pesticide delivery systems, cutting oils and drug delivery systems.
Microemulsions are crystal clear because the micellar particle size is too small to scatter visible light. The IUPAC definition of microemulsion is “a dispersion of water, oil and surfactant(s) that is an isotropic and thermodynamically stable system with dispersed domain diameter varying approximately from 1 to 100 nm, usually 10 to 50 nm.” In contrast to ordinary, white macroemulsions that usually require high shear conditions to form, microemulsions form upon simple mixing of the components, without the need for high-energy homogenization. Also, microemulsions of the present inventions are stable against phase separation and remain crystal clear in both concentrated and ready to use form.
The processes of the present inventions produce novel, crystal clear, stable, oil-in-water microemulsions using only food grade or excipient grade surfactants, edible botanical extracts or essential oils, and distilled or deionized water. No alcohols or sugars are used or needed and there are no additives that are not food grade quality. The microemulsion compositions and the preparation method thereof provides high manufacturing efficiency and yield with no by-products, low toxicity, low production cost, simple preparation process, good safety in production, storage, transportation and use process, good environmental protection performance, are biodegradable and have excellent antimicrobial efficacy.